1. Field of the Invention
The present invention relates to photolithography techniques and in particular to an exposure system, a test mask for flare testing, a method for evaluating lithography process, a method for evaluating exposure tools, a method for generating a corrected mask pattern, and a method for manufacturing a semiconductor device.
2. Description of the Related Art
As semiconductor devices continue to shrink in size over time, so do the individual circuit patterns. Accordingly, reproducing a designed circuit pattern on a wafer by exposing a mask has recently become difficult. Therefore, a method for controlling a line width of the projected pattern precisely is demanded. The optical proximity effect (OPE) is one of primary factors causing line width variations. The OPE depend on a pattern density or a periodicity of a region surrounding a feature of interest on a mask within a radius of some micrometers.
Further, the line width variations also depend on the local pattern density of the region surrounding the feature of interest within a radius of 10 to 1,000 micrometers. A mid range flare generated in an exposure tool, an acid diffusion into the air and accumulation on the resist surface during the post exposure bake (PEB) process and an unevenness of a concentration of the developer during the developing process are representative primary factors that depend on the local pattern density and cause unwanted line width variations.
In Japanese Patent Laid-Open Publication No. 2003-100624, a method for evaluating the flare intensity that is one of the primary factors of the line width variations depending on the pattern density of the mask is proposed. According to the method, a mask having a plurality of congruent rectangular patterns formed in a light shield layer and a transparent region is prepared. By measuring projected images of the rectangular patterns, the flare intensity is estimated.
However, the mask pattern is also manufactured by the lithography process such as the electron beam (EB) lithography, a resist development, and an etching process. Therefore, a feature of interest on the mask substrate may also vary dependent on the pattern density of a region surrounding the feature. Even though each size of the rectangular patterns formed in the shield layer and the transparent region is designed to be same, manufactured rectangular patterns may contain the manufacturing error in the size. Since measured sizes of the projected images of the rectangular patterns are affected by the manufacturing error, the measured size may not precisely reflect the primary factors causing the line width variations such as mid range flare.